Energy Changes 

Exothermic and Endothermic reactions

Exothermic = Energy is given out to the surroundings (temperature increases)

Endothermic = Energy is taken in from the surroundings (temperature decreases)

Temperature change - Required practical

Method :

1. Measure 25cm^3 of copper sulphate into a measuring cylinder and pour into a polystyrene cup
2. Using the thermometer measure the start temperature
3. Add 1 spatula of zinc powder to the cup with the copper sulphate
4. Stir the zinc and copper with thermometer
5. Measure the temperature, either leave for two minutes and measure or measure once it stops going up (highest temp)
6. Find the difference to calculate temperature change
7. Repeat with that metal minimum 3 times and find a mean average
8. Repeat steps 1-7 with a different metal

Example results

Risk assessment : Copper sulphate - is an irritant - wear goggles

Conclusion - Magnesium had the biggest temperature change of 21 degrees and aluminium had the smallest temperature change. Magnesium is the most reactive because it had the biggest temperature change

Aluminium is the least reactive because aluminium reacts with oxygen to form an outer layer of aluminium oxide. This is not reactive so the aluminium reacts less than we would expect

To improve what we’ve done we could use a thermometer that had a higher resolution (the smallest change equipment can measure) and could see a 0.1 change. We should repeat the test so that we could spot anomalies we could calculate a mean and it will reduce the effect of random errors.

Reversible reactions, Dynamic equilibrium and Le Chatelier’s principle

In reversible reaction, the products of the reaction can react to produce the original reactants

Dynamic equilibrium - Must be a reversible reaction, the rate of the forwards reaction is the same as the rate of the backwards reaction, the amount of each substance does not change everything is being used and formed at the same rate, happens in a closed system

Le Chatelier’s principle is the principle that if a change is made to a system at equilibrium the position of the equilibrium shifts to oppose the change

• An increase in temperature will favour the endothermic reaction
• A decrease in temperature will favour the exothermic reaction
• An increase in pressure will shift to the side with fewer molecules
• A decrease in pressure will shift to the side with more molecules
• If the concentration of a substance is increased, the equilibrium will shift to remove it

The Haber process

To produce ammonia you have to use three conditions: high pressure of 200 atmospheres, 450 degrees, and an iron catalyst

To make ammonia two elements are used

Nitrogen which is found in the air and hydrogen which is commonly taken from methane